The present invention relates to a system comprising a gear pump and a screw-type extruder for delivering elastomeric media, particularly caoutchouc, which comprises a screw and a screw casing, the screw-type extruder being arranged in front of the gear pump viewed in the delivery direction of the pumping medium. The invention relates to a use of the system as well as to two operating methods.
Gear pumps will be used particularly when a pumping medium of a constant flow rate is to be delivered at a comparatively high pressure. In particular, gear pumps are suitable for delivering very viscous media, among others, also elastomers. Thus, gear pumps have been used in the rubber industry for delivering caoutchouc mixtures.
When using a gear pump for delivering elastomeric media, the technological requirement consists of completely filling the tooth spaces of the gears in order to achieve a constant flow rate. In order to be able to fill the tooth spaces as completely as possible, it has been suggested to arrange a feeding system in front of the gear pump viewed in the delivery direction of the pumping medium.
Thus, reference is first made to Swiss Patent Document CH-A4-621 515 which describes an aggregate with spaced feeding rollers for generating a filling pressure in front of the gear pump. It was found that these known feeding devices, also called “torque feeders”, only insufficiently fill the gear pump or the tooth spaces of the gears.
Furthermore, from European Patent Document EP-A2-0 508 080, European Patent Document EP-A2-0 508 079 and from U.S. Pat. No. 5,156,781, systems are known in which a screw, which is also called an extruder, is arranged as a feeding device in front of a gear pump. Although a good filling of the tooth spaces of the gears is achieved by means of the extruder, often too much friction energy is charged in an uncontrollable manner into the pumping medium, which results in the danger of a cross-linking-on, particularly during the processing of caoutchouc.
The teaching disclosed in U.S. Pat. No. 5,156,781 differs from the above-mentioned published European patent documents in that a filter is provided between the extruder and the gear pump in the case of the first-mentioned patent document. As a result, the flow path for the pumping medium is significantly larger, whereby additional energy has to be charged into the pumping medium because, depending on the degree of contamination of the filter, a certain additional pressure drop must be overcome which occurs over the filter.
Furthermore, reference is made to German Published Patent Application Number DE-1 579 001, in which a screw-type extrusion machine is disclosed which, for modulating pressure fluctuations in the pumping medium, has a continuously tapering interior screw casing wall in the direction of the outlet end. The envelope of the screw body is constructed correspondingly. The modulation of occurring pressure fluctuations takes place by the axial displacement of the screw body in the screw casing, whereby the return flow of pumping medium is increased or reduced as a function of the position of the screw body in the screw casing. As in the above-mentioned known teachings, the charging of friction energy into the pumping medium takes place in an uncontrolled manner. For this reason, the above-mentioned disadvantages must also be expected in the case of this known teaching.
It is therefore an object of the present invention to provide a system in which the above-mentioned problems are avoided.
This object is achieved by a system of the above-noted type, wherein the screw casing has at least one conical part, and the screw has at least one tapering in an area of the conical part, and wherein the screw is axially displaceable in the screw casing for the controlled feeding of energy into the pumping medium. Advantageous further developments of the invention, a use as well as two operating methods are indicated herein and in the claims.
The invention has the following advantages: In that the feeding device or at least one of its main components, preferably a screw, is displaceable with respect to the screw casing and, as a result, the energy charged into the pumping medium by the feeding device can be controlled, the danger of a cross-linking-on of the pumping medium can be successfully prevented, or at least be considerably reduced.
In the following, the invention will be explained in detail by means of drawings in the manner of an example.